Neuromotor development in relation to birth weight in rabbits

The development of neuromotor patterns in relation to birth weight was studied in the rabbit, a perinatal brain developer. In order to induce intrauterine growth retardation and to increase the number of low birth weight rabbits, experimental ischemia to half the fetuses in each doe was achieved by total ligation of approximately 30% of spiral vessels to the placenta, during the last trimester of gestation. Following natural delivery, the rabbit pups were periodically observed for the appearance of eye-opening and righting reflex, and for the cessations of falling, circling and dragging of hind limbs. An index of neuromotor development was assigned to each rabbit by summing up the age (in days) of appearance of each of the neuromotor milestones. An association was found between low birth weight and delayed neuromotor development at 2 weeks of age. The most significant correlation was found between low birth weight and delayed disappearance of falling. The latter may represent incoordination as an expression of cerebellar dysfunction.

Relations between birth weight and learning ability in young rabbits

Performance on visual discrimination learning was studied in 41 rabbit pups mainly in relation to their birth weight, but also as functions of their neonatal motor development and weight gain between birth and training time. Partial placental vascular ligation was performed on some fetuses to increase the number of small-for-gestational-age pups. No relation was found between learning ability and either birth weight or rate of motor development. Low birth weight showed some association with slightly delayed motor development, but resulted in no lasting motor handicap. Between two subgroups of low birth weight pups, those who showed substantial weight gain by training time learned faster than those who remained relatively small.

Induction of tolerance in adult guinea-pigs by two antigen dosage levels and by antigenic competition

The effect of prior injection of increasing doses of dinitrophenylated bovine serum albumin (DNP-BSA) mixed in Freund's complete (FCA) or incomplete (IFA) adjuvants on the antibody response to a subsequent challenge with an optimal immunizing dose of DNP-BSA in FCA has been examined and compared with the effect of competition with the unrelated antigen bovine gamma-globulin (BGG). An unresponsive state was induced by pretreatments with either a minimal dose of antigen, a large antigen excess or a competitive mixture in FCA. The specificity of this unresponsiveness was ascertained by the normal response of pretreated animals to the unrelated antigen arsanilic-human albumin (ARS-HSA). Prior injection of either a minimal dose (0,2 mug), an antigen excess (20 mg) of DNP-BSA or an optimal dose (20 mug) of DNP-BSA mixed with an excess of BGG, incorporated in IFA, also induced a specific tolerance to DNP-BSA. The former treatment induced a low zone tolerance whereas both later treatments induced a high zone tolerance.

Experimental intrauterine growth retardation

The effects of experimental intrauterine growth retardation on subsequent fetal development, especially with respect to brain development, were studied in a new animal model. The rabbit was chosen since it has a perinatal pattern of brain development similar to that of the human. Experimental ischemia was induced during the last trimester by ligation of spiral arterioles and the differential effects on fetal development at term (30th gestational day) are reported. Specific brain regions were examined for wet weight, total cell number (DNA) and total protein content. Highly significant decreases in all these parameters were found in both the cortex and cerebellum following experimental intrauterine growth retardation; these two organs were differentially affected. The prospects and advantages of using this animal model for the study of the postnatal "catch-up growth" are discussed.

Inhibition of immunological components by antigenic competition and other immuno-depressing procedures

Four experimental procedures leading to lower antibody production, namely administration of a minute amount of antigen or excess of antigen, competition with an unrelated antigen and treatment with methotrexate, were studied for their effect on each of the forms of immunological responses in guinea-pigs to a DNP-BSA conjugate.

It was found that delayed hypersensitivity and 2-ME sensitive antibody production were more reduced by administration of excess of antigen or by competition than by giving a minute amount of antigen or methotrexate. On the other hand, IgG₁ production was more suppressed in the groups receiving minute amounts of antigen or methotrexate treatment than in those given excess of antigen or subjected to competition. IgG₂ production was markedly reduced in all four groups of animals. However, excess of antigen and competition changed the kinetics of both total antibody and IgG antibody production (peak on day 20 after immunization). The peak of total as well as IgG₂ antibody-production in the groups given a minute amount of antigen or methotrexate, was on day 35, the same as in optimally immunized animals.

These results suggest that a common mechanism for reduction of the immune response may be responsible for the excess of antigen and competition effects on one hand and the minute amount of antigen and methotrexate effects on the other. Competition with an unrelated antigen and excess of the same antigen could both act on the same effector cell. Methotrexate could act not only by killing a proportion of immunologically competent cells, but also by lowering their sensitivity to stimulation by antigen.

The production and affinity of anti-hapten antibody under the influence of various inhibitory conditions

The effects of four experimental conditions leading to lower antibody production (minute amount of antigen, excess of antigen, treatment with methotrexate and competition with an unrelated antigen) on the amount and affinity of antibody produced by injecting an optimal immunizing amount of dinitrophenylated bovine serum albumin (DNP-BSA) in adult guinea-pigs were compared.

Adequate use of these four conditions resulted in a rather similar degree of inhibition, antibody production averaging 15 per cent of that produced by optimally stimulated animals. Affinity for the hapten DNP-ε-aminocaproic acid of the antibody produced following stimulation with a minute amount of antigen or following treatment with methotrexate was found to be closely similar to the affinity of antibodies produced by optimally stimulated animals, Both immunization with an excess of antigen and immunization with an optimal amount of DNP-BSA mixed with an excess of an unrelated antigen (bovine γ-globulin), led to the production of antibody of low affinity.

These results seem to indicate that the competing antigen interfered with the test antigen at the level of the antibody producing cell.

Selective immune reactivity to DNP-poly-L-lysine in randomly bred guinea-pigs

The specific immune response towards the synthetic antigen DNP—p(Lys) in randomly bred guinea-pigs has been investigated. A full immunological response, namely delayed hypersensitivity, PCA reactive, complement fixing and mercaptoethanol sensitive antibodies was obtained in nearly half the animals. The other half also showed an immune response restricted, however, to complement fixing and mercaptoethanol sensitive antibodies. Genetic heterogeneity of these animals with respect to immunization to DNP—p(Lys) was thus found to be reflected in the type of immune response induced rather than in an all or none reactivity.